Kathleen Sullivan is a noted constitutional scholar who has argued cases before the Supreme Court. Until recently, she was dean of Stanford Law School. In legal circles, she has been talked about as a potential Democratic nominee for the Supreme Court. But Ms. Sullivan recently became the latest prominent victim of California's notoriously difficult bar exam. Last month, the state sent out the results of its July test to 8,343 aspiring and already-practicing lawyers. More than half failed -- including Ms. Sullivan.

Although she is licensed to practice law in New York and Massachusetts, Ms. Sullivan was taking the California exam for the first time after joining a Los Angeles-based firm as an appellate specialist.

The California bar exam has created misery for thousands of aspiring and practicing lawyers. Former California Gov. Jerry Brown passed on his second try, while former Gov. Pete Wilson needed four attempts. The recently elected mayor of Los Angeles, Antonio R. Villaraigosa, never did pass the bar after failing four times.

But it's unusual for the exam to claim a top-notch constitutional lawyer at the peak of her game. "She is a rock star," says William Urquhart, who last year recruited Ms. Sullivan to join his firm, Quinn Emanuel Urquhart Oliver & Hedges LLP. "Practically every lawyer in the U.S. knows who Kathleen Sullivan is." If anyone should have passed, Mr. Urquhart says, it is Ms. Sullivan. "The problem is not with Kathleen Sullivan, it is with the person who drafted the exam or the person who graded it."

Ms. Sullivan, 50 years old, did not return phone and email messages seeking comment. Her firm said she wasn't reachable over the weekend because she was at a remote location.

Mr. Urquhart says he does not know Ms. Sullivan's score, but knows she spent little time preparing because she was inundated with work for the firm and Stanford Law School, where she now runs the school's constitutional law center. Ms. Sullivan plans to take the test again, according to Mr. Urquhart. "She'll prepare more next time," he says. "My advice to her is that she should look at 15 bar questions and 15 sample, perfect answers. That is all she'll need to pass."

The California test, by all accounts, is tough. It lasts three days, as compared with two or 2½-day exams in most states. Only one state -- Delaware -- has a higher minimum passing score. According to the National Conference of Bar Examiners, just 44% of those taking the California bar in 2004 passed the exam, the lowest percentage in the country, versus a national average of 64%.

Like many professions, lawyers are regulated by the states, and nearly every state requires passage of a bar exam for attorneys to practice law. Some states grant reciprocity to out-of-state lawyers. California does not; to be licensed in the state, one must pass the California bar exam. This July's version of the California test aimed at lawyers licensed in other states -- like Ms. Sullivan -- claimed an unusually high percentage of victims.

The two-day test, which is identical to the longer exam but omits a long multiple-choice section, had just a 28% passage rate in July, an astoundingly low figure that state bar officials are at a loss to explain. Out-of-state lawyers can take the full three-day exam if they choose.

Critics say the test is capricious, unreliable and a poor measure of future lawyering skills. Some also complain that California's system serves to protect the state's lawyers by excluding competition from out-of-state attorneys. There has been some loosening of the rules. California adopted rules last year permitting certain classes of lawyers to practice in the state without having to take the bar.

Gayle Murphy, the senior executive for admissions for the State Bar of California, says that the purpose of the bar exam is to protect the public, not to restrain competition. Great efforts are taken to make sure exam grading is fair, including use of multiple graders, she says. The exam includes six essays and two written performance tests. Each written part is assigned a separate grader. Test-takers who are close to the passing line are assigned nine more graders, so a borderline exam will have as many as 17 graders.

One reason for California's high failure rate, Ms. Murphy says, is that graduates of unaccredited and correspondence law schools are allowed in California to take the test. California's pass rate for ABA-approved schools is in line with those of other states, Ms. Murphy says. She says a possible reason for failures by practicing lawyers is that they simply don't have enough time to put in the requisite studying hours. Attending a premier law school doesn't guarantee success: former Gov. Wilson got his law degree from Berkeley, while former Gov. Brown went to Yale.

Aundrea Newsome, an attorney in Hermosa Beach, Calif., who passed the July test, limited her prep time to two months, but she worked eight to 10 hours a day, every day, during that stretch. "That is standard," she says. "You make a deal with the devil and give up two months of your life to pass."

Ms. Newsome, who graduated from the University of Southern California Law School in May, says preparing for the exam requires studying so many different legal fields, including such arcane topics as 18th-century criminal common law, that practical knowledge or even mastery of several legal subjects is not enough.

Robert Pfister, who was already licensed in Indiana, Connecticut and New York, also found the experience grueling. After the first morning of the exam, "you feel like your hand will fall off from writing so much," says Mr. Pfister, an associate with Simpson Thacher & Bartlett LLP who passed the July exam in California. "After the second day, you just want to go home and sleep. But then you have to come back for a third day."

Mr. Pfister, who handles securities-fraud cases and had been practicing law for about four years before taking the California bar, recalls one question where he was asked to parse the law that would apply to a disabled child who was seeking to move to a housing complex. "You can be the greatest personal-injury lawyer in the country, or mergers and acquisitions lawyer," he says. "But the stuff they give you is often some area of law you haven't dealt with."

Former Gov. Wilson describes his need to take the bar exam four times as "frustrating." He blames his difficulties on his penmanship, which he says was not messy, but very slow. "To put it in the simplest terms, if I had not learned to type, I would never have passed it," says Mr. Wilson.

A spokesman for former Gov. Brown, who is currently mayor of Oakland, Calif., says several of his classmates from Yale also failed the exam, some of whom went on to be judges and prominent lawyers.

A native of New York City, Ms. Sullivan has an undergraduate degree from Cornell University and a law degree from Harvard University. She taught at both Stanford and Harvard before becoming dean of Stanford's law school in 1999. The author of a leading constitutional-law casebook, Ms. Sullivan has argued several cases before the Supreme Court. Earlier this spring, the nation's highest court ruled in favor of one of her clients, a California winegrowers' group, striking down state laws that restricted direct sales from vineyards to consumers.

Last year, after announcing she would step down from her Stanford post, Ms. Sullivan joined the Silicon Valley office of Quinn Emanuel Urquhart to head a new appellate practice.

Ms. Sullivan is unlikely to need as many attempts as Maxcy Dean Filer, who may hold the California bar endurance record, having passed in 1991 after 47 unsuccessful tries. The Compton, Calif., man, who says he'll practice any kind of law that "comes through the door -- except probate and bankruptcy," says he always tried to psych himself up before taking the test by repeating, "I didn't fail the bar, the bar failed me."